DE 10 2004 002 307 A1 discloses machines capable of processing sheet-shaped material, whereby the material is delivered in stacks, singulated in sheet feeders and transported to the next machine downstream in the process. For this purpose, a main stack is positioned on a main stack carrier in a stack-acquiring position. A conveying system, preferably in the form of lifting chains, is connected with a driving mechanism and engages the main stack carrier. The sheet-shaped material is singulated from the top of the main stack by the separating and conveying device and transported to the next machine downstream. At the same time, the main stack carrier is raised periodically or continuously. Once the main stack is singulated, the main stack carrier is returned to its starting position at or directly above floor level, in preparation to take a new stack.
In order to facilitate a continuous operation, it is customary to provide an auxiliary stack carrier, which conveys an auxiliary stack of sheets periodically or continuously to the separating and conveying device. While the auxiliary stack carrier is conveying the auxiliary stacks, the main stack carrier is brought back to its starting position for taking of a subsequent stack of sheets. After the main stack carrier has taken the subsequent stack of sheets, the main stack carrier is raised by the conveying system and the subsequent stack of sheets is combined with the auxiliary stack conveyed by the auxiliary stack carrier and the assembled stack is taken to the separating and conveying device.
For sheet feeders of a smaller format, the maximum weight of the stack is limited by the area available on the stack carrier and limited in height by the position of the separating and conveying device. The conveying system, its driving mechanism and the statics of the sheet feeder frame are designed from the aspect of the desired maximum stack weight. Similarly, large format sheet feeders are characterized by the large area available on the stack carrier, the large distance between the separating mechanism and conveying mechanism and floor level, and the wide spectrum of materials which may be processed on such machines. However, because of worker safety considerations, it is necessary to start out from the largest possible stack weight when designing the conveying system, the driving mechanism and the static for large format sheet feeders. Because the maximum stack weight must be taken into consideration and because the feeders must incorporate necessary safety features, the related safety components of the feeder are overdimensioned resulting in high manufacturing costs. In view of the fact that stacks with the maximum conceivable weight are processed only in isolated cases, such a sheet feeder design is not economically practical.